I had a similar problem with my home-brew design. I found a "blip" with 1 second period on the output of the error amplifier. I couldn't eliminate it with extra power supply filtering. The high gain of the error amplifier picked up a very small voltage that developed on "ground". I solved it by supplying the phase detector and error amplifier with a separate 5 V supply. I tied the ground pin of the new 5 V regulator very close to the phase detector ground pin. Bob Q.
----- Original Message ----- From: "Bruce Griffiths" <[EMAIL PROTECTED]> To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com> Sent: Tuesday, August 05, 2008 3:43 PM Subject: Re: [time-nuts] Power supply for Thunderbolt > David C. Partridge wrote: >> I'm using the Meanwell T30-B, but Tom van Baak's test on this shows a bit >> of >> phase noise at 1Hz offset which is a tad nasty: >> >> http://www.leapsecond.com/pages/tbolt/noise.htm >> >> I'm wondering if this can be reduced with a bit of extra de-coupling on >> the >> 5V supply, but haven't got round to scoping the 5V supply to see what >> happens every second (presumably as the output is sent to the serial >> port). >> >> Cheers >> Dave >> >> > Dave > > If phase noise at 1Hz offset is a problem you will probably need a > power supply filter with cutoff frequency well below 1Hz to make any > discernable difference. > Since the an RC filter will produce a voltage drop in the 5V supply the > resistor value will have to be kept small and the capacitor value > correspondingly large (several farads). > It may be possible to stack 3 low ESR super capacitors in series > (maximum voltage rating is around 2v -2.5V those with higher ratings are > actually series connected stacks) to do this but this is a relatively > expensive proposition. > > Alternatively a modified version of the Wenzel active power supply > filter could be used if a series stack of 2 low ESR supercaps were > substituted for the capacitor connected from the supply to the > transistor base. The modified circuit stabilises the transistor's > effective emitter resistance and keeps the active filter dc current low. > > It may also be possible to use a variation of Wenzel's opamp augmented > active filter scheme, however the filter low frequency cutoff will have > to be well below 1Hz for it to be effective. > > Bruce > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
